I don't know if any are currently made, but a great many .25 ACP caliber revolvers were produced in the early part of the 20th century, mostly in France and Belgium. Most were folding trigger revolvers, with rod ejection. There was also a German gun, called the "Reform" pistol, which used a block of four barrels stacked vertically. As each barrel was fired, a device like a revolver "hand" indexed the block up one barrel until all four had been fired. Ejection of empties in the top three barrels was accomplished by having a hole between barrels so the gas from the second barrel blew into the first barrel, blowing the empty case out to the rear. A large hammer deflected the ejected case so it did not strike the firer. The empty case in the bottom barrel had to be removed by hand.
Jim